How Docker Compose Works: Compose File and Application Model

--- title: How Compose works weight: 10 description: Understand how Compose works and the Compose application model with an illustrative example keywords: compose, docker compose, compose specification, compose model aliases: - /compose/compose-file/02-model/ - /compose/compose-yaml-file/ - /compose/compose-application-model/ --- With Docker Compose you use a YAML configuration file, known as the [Compose file](#the-compose-file), to configure your application’s services, and then you create and start all the services from your configuration with the [Compose CLI](#cli). The Compose file, or `compose.yaml` file, follows the rules provided by the [Compose Specification](/reference/compose-file/_index.md) in how to define multi-container applications. This is the Docker Compose implementation of the formal [Compose Specification](https://github.com/compose-spec/compose-spec). {{< accordion title="The Compose application model" >}} Computing components of an application are defined as [services](/reference/compose-file/services.md). A service is an abstract concept implemented on platforms by running the same container image, and configuration, one or more times. Services communicate with each other through [networks](/reference/compose-file/networks.md). In the Compose Specification, a network is a platform capability abstraction to establish an IP route between containers within services connected together. Services store and share persistent data into [volumes](/reference/compose-file/volumes.md). The Specification describes such a persistent data as a high-level filesystem mount with global options. Some services require configuration data that is dependent on the runtime or platform. For this, the Specification defines a dedicated [configs](/reference/compose-file/configs.md) concept. From a service container point of view, configs are comparable to volumes, in that they are files mounted into the container. But the actual definition involves distinct platform resources and services, which are abstracted by this type. A [secret](/reference/compose-file/secrets.md) is a specific flavor of configuration data for sensitive data that should not be exposed without security considerations. Secrets are made available to services as files mounted into their containers, but the platform-specific resources to provide sensitive data are specific enough to deserve a distinct concept and definition within the Compose Specification. > [!NOTE] > > With volumes, configs and secrets you can have a simple declaration at the top-level and then add more platform-specific information at the service level. A project is an individual deployment of an application specification on a platform. A project's name, set with the top-level [`name`](/reference/compose-file/version-and-name.md) attribute, is used to group resources together and isolate them from other applications or other installation of the same Compose-specified application with distinct parameters. If you are creating resources on a platform, you must prefix resource names by project and set the label `com.docker.compose.project`. Compose offers a way for you to set a custom project name and override this name, so that the same `compose.yaml` file can be deployed twice on the same infrastructure, without changes, by just passing a distinct name. {{< /accordion >}} ## The Compose file The default path for a Compose file is `compose.yaml` (preferred) or `compose.yml` that is placed in the working directory. Compose also supports `docker-compose.yaml` and `docker-compose.yml` for backwards compatibility of earlier versions. If both files exist, Compose prefers the canonical `compose.yaml`. You can use [fragments](/reference/compose-file/fragments.md) and [extensions](/reference/compose-file/extension.md) to keep your Compose file efficient and easy to maintain. Multiple Compose files can be [merged](/reference/compose-file/merge.md) together to define the application model. The combination of YAML files is implemented by appending or overriding YAML elements based on the Compose file order you set.

Docker Compose uses a YAML configuration file (compose.yaml) to define an application's services. This file adheres to the Compose Specification, defining services, networks, volumes, configs, and secrets. A project represents a deployment of the application on a platform, with a name to isolate resources. The Compose file can be split using fragments and extensions, and multiple files can be merged together.